"Dr. Livingstone, I presume." Welsh-born American journalist Henry M. Stanley (1841-1904) uttered those words, or so he claimed, upon tracking down the Scottish missionary and long-missing explorer Stanley Livingstone beside Lake Tanganyika in central Africa in 1871. Stanley continued to investigate Africa on a series of expeditions that he described in "Through the Dark Continent" -- journeys that later drew criticism for Stanley's harsh dealings with the tribesmen he encountered. But there was no question of his courage and energy in the face of extreme hardship. This book's subtitle alone -- "The Sources of the Nile, Around the Great Lakes of Equatorial Africa, and Down the Livingstone River to the Atlantic Ocean" -- is enough to quicken the pulse.